Method of manufacturing common rails

A method of manufacturing common rails, having the steps of forming at least one branch hole in an axially extending circumferential wall of a main tubular rail having a flow passage in an axially extending inner portion thereof;

• forming on an inner circumferential surface of the branch hole an outwardly opened pressure receiving seat surface to which a branch pipe having a flow passage communicating with the flow passage in the main tubular rail is joined;
• engaging a pressure seat surface, which is formed on a joint head on an end portion of the branch pipe, with the pressure receiving seat surface;
• and screwing on each other a separately formed metal joint fixed to the main tubular rail and a tightening nut fitted around the branch pipe in advance, to thereby fasten and join the branch pipe to the main tubular rail by a pressure occurring due to screwing force exerted on a bent surface of a neck portion of the joint head, wherein, before the step of forming the branch hole, the method comprises the steps of:
• forming a bottomed lower hole in advance in a portion of the main tubular rail that will subsequently define the branch hole,
• generating residual compressive stress in a circumferential part of an end portion of the bottomed lower hole substantially adjacent the flow passage of the main tubular rail by applying a pressing force from the outside to the bottomed lower hole in an axial direction thereof by an external pressure system, and then
• cutting off a fine defect occurring in the bottomed lower hole.

A method of manufacturing common rails, having the steps of forming at least one joint hollow in an axially extending circumferential wall of a block rail having a flow passage in an axially extending inner portion thereof, forming in the at least one joint hollow a branch hole communicating with the flow passage and having a pressure receiving seat surface, forming a pressure seat surface on a joint head provided at an end portion of a branch pipe having therein a flow passage for communicating with the flow passage in the block rail, engaging the pressure seat surface with the pressure receiving seat surface, screwing a tightening nut, which is fitted around the branch pipe in advance, into the joint hollow, and fastening and joining the branch pipe to the block rail by a pressure occurring due to screwing force exerted on a bent surface of a neck portion of the joint head, wherein, before the step of forming the branch hole, the method comprises the steps of:

• forming a bottomed lower hole in the portion of the block rail which will define the branch hole;
• generating residual compressive stress in a circumferential part of the bottomed lower hole substantially adjacent the flow passage in the block rail by applying a pressing force from the outside to the bottomed lower hole in the axial direction thereof by an external pressure system, and then
• cutting off a fine defect occurring in the bottomed lower hole.

A method of manufacturing common rails for a fluid system, said method comprising:

• providing a main rail having a peripheral wall and an axial flow passage extending through the peripheral wall and having an outer peripheral surface formed on the peripheral wall and spaced from the axial flow passage;
• forming in the peripheral wall a lower hole aligned substantially transverse to the axial flow passage and extending from the outer peripheral surface to a bottom at a location in the peripheral wall spaced from the axial flow passage;
• applying a pressing force to the bottom of the lower hole, the pressing force being of a sufficient magnitude to generate a residual compressive stress in the peripheral wall at location substantially adjacent and between the bottom of the lower hole and the axial flow passage;
• and
• boring the peripheral wall at locations substantially concentric with lower hole for forming the lower hole into a branch hole that communicates with the axial flow passage and for removing defects in the peripheral wall caused by the step of applying a pressing force, whereby the residual compressive stress and the removal of defect enhances durability of the common rail.